The present invention relates to a layer arrangement for electro-optical apparatuses that contains an electrophosphorescent material, and electroluminescent arrangements that comprise this layer arrangement.
Electroluminescent arrangements have a wide range of uses, for example, in the production of screens or displays. There has recently been increasing interest in emissive displays and display apparatuses, particularly utilizing electrophosphorescence for increasing the light efficiency yield (cf. Baldo et al., Appl. Phys. Lett., Vol. 75, No. 1, 4, 1999; WO 00/70,655 A2).
Triplet-based emission of light is known by the term phosphorescence (WO 00/70,655 A2). The advantage of phosphorescence over fluorescence is that the major part of triplet-based excitons that are formed by recombination of holes and electrons in an electroluminescent layer are available for energy transfer with luminescence.
In order to ensure as high an efficiency as possible of an emitting arrangement, a tailored layer structure of the electroluminescent arrangement is required. WO 00/70,655 A2 discloses such a layer structure, which, however, is still not optimum both with respect to long-term stability and with respect to the external quantum yield. Thus, for example, a hole injection layer is applied by a vacuum process, i.e., by vapor deposition of a low molecular weight amine, to a substrate which is coated with indium tin oxide (ITO). The inherent roughness of the ITO surface is inevitably transferred to the substrate and is retained thereon. However, even roughness have a very adverse effect during operation of an electroluminescent arrangement since it leads to voltage peaks that result in faster aging and degradation of the layer structure.
WO 00/70,655 A2 describes organic light emitting diodes (OLEDs) that have a hole conductor layer and an electron transport layer. These layers contain compounds, e.g. tris(8-hydroxyquinoline)aluminum (Alq3), which can be applied only by a complicated and expensive vapor deposition process. The much simpler and established processing from solution by means of spin coating, casting methods, or inkjet methods would be desirable.
According to WO 00/70,655 A2, polymer films, such as polycarbonate or other transparent polymers, are used as transparent substrates for the production of the OLEDs. These substrates are provided with a conductive layer, preferably indium tin oxide (ITO). However, the excessively great roughness of the conductive layer, which may lead to short-circuits during operation and to the high level of waste during production, is disadvantageous. As a result of the production, customary inorganic conductive layers on plastic substrates always have greater roughness than on glass. Furthermore, inorganic conductive layers, such as ITO, are brittle, so that cracks occur on the flexible substrates, due to a different coefficient of expansion or extensibility and toughness, and may lead to a break in the electrical conductivity. This occurs in particular during the storage and/or handling of rolled-up substrates, such as, for example, ITO-PET (PET is polyethylene terephthalate) for roll-to-roll processes.
An object of the present invention was therefore the development of novel layer arrangements that permit the emission of light from excited triplet states and that do not have the stated disadvantages.
In order to achieve the object, a layer of an organic conductive polymer system is applied directly to the already present conductive layer (e.g., ITO) of the substrate. By applying the conductive polymer system, surface roughness of the conductive layer on the substrate, particularly on plastic substrates, is compensated. Furthermore, the polymer system covers any cracks present. Through its extensibility and toughness, it ensures that, even after handling of the layer system according to the invention, any cracks present remain covered by conductive paths and the surface conductivity is not broken.